1. Field of the Invention
The present invention relates to an individual identification apparatus for confirming identities of individuals with using a pattern recognition technique.
2. Description of the Related Art
Recently, confirmation of identities of individuals is required in order to manage entrance and exit of individuals in and out of restricted areas and to prevent free access to important equipment. Individual identification apparatuses have been proposed to identify each individual under investigation with a specific individual on record. The person under investigation will be referred to as an "arbitrary individual" hereinafter.
Fingerprints, palm prints, retinas, and voices, for example, are unique for each individual. The individual identification apparatuses therefore generally compare such a unique characteristic of an arbitrary person with a corresponding characteristic of the specific person.
It is noted that the fingerprint has attracted attention because it is easily handled and it can allow the individual identification apparatus to provide a high recognition accuracy. According to a conventional fingerprint identification method, the individual identification apparatus extracts features (minutiae) from fingerprints. The features include character points such as ending and turning points of ridges in the fingerprints. Confirmation of the individual's identity is performed based on those features extracted from the fingerprints.
According to this method, however, fingerprints have to be subjected to complicated preprocessings in order to accurately extract features from the fingerprints. A large number of features have to be extracted from the fingerprints in order to enhance recognition accuracy.
On the other hand, it is still desirable that the number of features be small so that the recognition operation can be attained in a short period of time. These conflicting demands make it difficult to provide an individual identification apparatus which can perform its recognition operation with high accuracy but still within a short period of time.
Especially, confirming a mismatch between different individuals generally requires a longer time period than when confirming a match between identical individuals as described below.
According to the conventional method, when one feature is extracted from the arbitrary person s fingerprint, the extracted feature is compared with a corresponding feature of the specific person's fingerprint. The features in the arbitrary person's fingerprint are subjected one by one to this extracting-and-comparing operation. In order to judge a mismatch between the arbitrary person and the specific person, a predetermined large number of features have to be subjected to the extracting-and-comparing operations. The number of features, in the arbitrary person's fingerprint, that match the corresponding features of the specific person's fingerprint is counted. The mismatch between the arbitrary person and the specific person is confirmed when the number of those matching features is less than a predetermined threshold.
A match between the arbitrary person and the specific person is confirmed when the number of the matching features reaches the predetermined threshold. It is noted, however, that the number of the matching features will possibly reach the predetermined threshold before the extracting-and-matching operations are completed for all the predetermined number of features. In this case, it becomes unnecessary to extract remaining features from the arbitrary person's fingerprint. Thus, confirming a match between identical individuals generally needs extraction of less features than when confirming a mismatch between different individuals. In other words, confirming a mismatch between different individuals generally requires a longer time period than when confirming a match between identical individuals.